Method and arrangement for heat treatment of substrates

ABSTRACT

To provide a method and an arrangement for heat treatment of substrates which allow continuously adjustable cooling rates over a wide temperature range with simultaneously largely homogeneous temperature distribution over the area of the heating/cooling plate, a cooling/heating plate is provided containing a multiplicity of cooling/heating pipes running parallel to one another. Each cooling/heating pipe comprises an outer pipe, an inner pipe which can carry a flow, and an interspace between them which can carry a flow. Each inner pipe is connected to a supply line for water and each interspace is connected to a supply line for air, with water and air being routed simultaneously though the cooling/heating plate.

The invention concerns a method for thermal treatment of substrates, as well as an arrangement for execution of the method.

RTP (rapid thermal processes) are often used in heat treatment of substrates, for example, semiconductor wafers, solar cells, equipped circuit boards, etc., i.e., processes with rapid temperature changes, in order to impart certain properties to the treated materials or to control soldering processes or quite simply to drastically shorten the duration of the thermal processes.

Heating ordinarily occurs by radiation heating and/or a cooling/heating plate on which the substrates being treated lie or are arranged at limited, optionally variable spacing above it.

Very high ramp rates of the temperature change, if possible also with an adjustable ramp curve, must be achieved during treatment of substrates with RTP processes.

To achieve this the cooling/heating plates 1, consisting of brass, aluminum, stainless steel, gray cast iron, etc., are equipped with a cooling tube 2, which is passed through meander-like (FIG. 1, prior art) and through which compressed air or water flows. For this purpose the cooling tube 2 is provided with a connection 3 for water supply and a connection 4 for water discharge. A cooling rate of up to 5 K/min can be achieved with compressed air and a cooling rate of >20 K/min with water.

A method and an apparatus for heat treatment of wafer-like substrates is apparent from DE 102 60 672 A1, in which a heating/cooling plate traversed by a fluid is provided to heat and cool and a substrate. The corresponding fluid can then be held statically within the heating/cooling plate or continuously passed through it, specifically for cooling of the heating/cooling plate, as required.

A range of temperature change of 15 K/min lies between cooling with pure air and cooling with water. This results in the problem that stepless cooling with ramp rates in the range from −1 to −100 K/min cannot be achieved. Moreover, the meandering passage of the cooling tubes through the cooling/heating plate does not provide acceptable homogeneity of the temperature distribution on the surface of the plate even with respect to higher soldering temperatures above 450° C. A temperature homogeneity of 150 K over the plate at 650 K is reached during meander cooling.

This results in the task of devising a method and arrangement for thermal treatment of substrates with which continuously adjustable cooling rates can be achieved over a broad temperature range with essentially homogeneous temperature distribution at the same time over the surface of the heating/cooling plate.

The task underlying the invention is solved according to the method in that two media of different thermal conductivity are simultaneously passed through a cooling/heating plate so that a first medium of higher thermal conductivity is fully enclosed during flow through the cooling/heating plate by at least a second medium of lower thermal conductivity.

When the cooling/heating plate is used as a heating plate, the attainable upper temperature is naturally dependent on the first medium, whereas when the cooling/heating plate is used as a cooling plate it can be cooled down from much higher temperatures, as occur, for example, during soldering processes.

In a first embodiment of the invention, the flow rate and direction of both media through the cooling/heating plate can be adjusted independently of each other so that ramp rates in the range from −1 to −100 K/min are attainable in fine steps.

The first medium of higher thermal conductivity is a liquid, preferably water, and the second medium of lower thermal conductivity is a gas, preferably air.

In a special embodiment of the invention the first medium is either cooled or heated as required for introduction to the cooling/heating plate.

Another embodiment of the invention is characterized by the fact that the cooling or heating power is controlled in stepless fashion from the minimum to the attainable maximum by volume control of the second medium.

Finally, it is prescribed that the first medium is passed continuously or in pulses through the cooling/heating plate.

For a case in which a particularly high cooling rate is to be achieved, the second medium is at least temporarily replaced by the first medium.

The task underlying the invention is also solved by a device, characterized by the fact that a number of cooling/heating tubes are arranged parallel to each other within a cooling/heating plate, each cooling/heating tube consisting of an outer tube, a traversable inner tube and a traversable intermediate space and that each inner tube is connected to a feed for a medium of a first thermal conductivity and each intermediate space is connected to a feed for a medium of a second thermal conductivity.

In a modification of the invention the feeds for the media of different thermal conductivity each consist of a distributor device with media feed so that the media are uniformly distributed over all parallel cooling strands.

The distributor device for the medium of first or second thermal conductivity has a trapezoidal inner space in which an also trapezoidal volume element with smaller dimensions is arranged. The volume element ensures uniform distribution of the media in the inner tubes and intermediate spaces between the corresponding inner and outer tube.

The inner tube is finally connected to a water feed as medium of first thermal conductivity and the intermediate space is connected to an air feed as medium of second thermal conductivity.

The invention will be explained further below on a practical example. In the corresponding figures of the drawing:

FIG. 1: shows a cooling/heating plate according to the prior art;

FIG. 2: shows a cooling/heating plate according to the invention with parallel cooling/heating tubes;

FIG. 3: shows a schematic view of a device for uniform distribution of air and water in the cooling/heating tubes according to FIG. 2 and

FIG. 4: shows a schematic view of a cooling/heating tube.

According to the invention a number of cooling/heating tubes 5 are passed parallel through the cooling/heating plate 1 and the heating/cooling medium water/air is uniformly distributed over all parallel cooling strands via a distributor device 6 with media feed 7. To achieve this, jacketed cooling/heating tubes 5 are used in which an intermediate space 10 is arranged between the outer wall of the inner tube 8 and the outer tube 9 (FIG. 4). The substrates being cooled (not shown), such as silicon wafers or the like, lie on the cooling/heating plate 1.

Cooling occurs with water, which is passed through the inner tube 8, during which damping of the cooling power is conducted simultaneously by passing air through the intermediate space 10. The underlying idea is therefore to use the high cooling power of water (medium with first thermal conductivity) and regulate it with the damping effect of air (medium with second thermal conductivity). It is understood that defined heating can also be accomplished and supported in the same way by passing heated water into the inner tube, in which case heating and cooling can alternate with each other.

For simultaneous distribution of air and water to the parallel cooling/heating tubes 5 a special trapezoidal distributor device 6 with an also trapezoidal volume element 11 situated inside with smaller dimensions is used (FIG. 3). This distributor device 6 bridges the parallel cooling/heating tubes 5 on both sides of the cooling/heating plate (FIG. 2) and ensures uniform water distribution in all cooling/heating tubes 5 so that a uniform temperature distribution is achieved on the entire cooling/heating plate 1.

The cooling medium water then flows through the inner tube 8 in a uniform stream or also in pulsed fashion. The air flowing through the intermediate space 10 attenuates heat transfer and therefore dampens the cooling power of the water. Owing to the fact that numerous parallel cooling/heating tubes 5 are used, a higher water throughput, connected with very high maximum cooling power, can be achieved. Flow of the tube media through the cooling/heating tubes 5 can occur in the same or opposite direction.

The cooling power can be controlled in stepless fashion according to the invention by volume control of the air from the minimum to the attainable maximum.

If very high cooling rates are required, the intermediate space 10 around the inner tubes 8 can also be fully flooded with water.

Cooling rates from −1 K/min to −100 K/min can be continuously controlled with the solution according to the invention. The temperature homogeneity over the surface of the heating/cooling plate is about 35 K.

A particular advantage of this invention is seen in the fact that the method is easy to manage and that the media water and (compressed) air are available everywhere among users anyway.

LIST OF REFERENCE NUMBERS

-   1 Cooling/heating plate -   2 Cooling tube -   3 Connection -   4 Connection -   5 Cooling/heating tube -   6 Distributor device -   7 Media feed -   8 Inner tube -   9 Outer tube -   10 Intermediate space -   11 Volume element 

1. Method for thermal treatment of substrates by a cooling/heating plate, wherein two media of different thermal conductivity are simultaneously passed through the cooling/heating plate so that a first medium of higher thermal conductivity is fully enclosed by at least a second medium of lower thermal conductivity during flow through the cooling/heating plate.
 2. Method according to claim 1, wherein flow rate and direction of both media through the cooling/heating plate are adjustable independently of each other.
 3. Method according to claim 1, wherein a liquid is used as the first medium of higher thermal conductivity.
 4. Method according to claim 3, wherein water is used as the first medium.
 5. Method according to claim 1, wherein a gas is used as the second medium of lower thermal conductivity.
 6. Method according to claim 5, wherein air is used as the second medium.
 7. Method according claim 1, wherein the first medium is cooled or heated for introduction to the cooling/heating plate.
 8. Method according to claim 1, wherein cooling or heating power of the cooling/heating plate is controlled in stepless fashion from a minimum to an attainable maximum by volume control of the second medium.
 9. Method according to claim 1, wherein the first medium is passed through the cooling/heating plate continuously or in pulsed fashion.
 10. Method according to claim 1, wherein the second medium is at least temporarily replaced by the first medium.
 11. Device for thermal treatment of substrates by a cooling/heating plate, comprising a number of cooling/heating tubes arranged parallel to each other within the cooling/heating plate, each cooling/heating tube comprising an outer tube, a traversable inner tube and a traversable intermediate space, and wherein each inner tube is connected to a feed for a medium of a first thermal conductivity and each intermediate space is connected to a feed for a medium of a second thermal conductivity.
 12. Device according to claim 11, wherein the feeds for each medium comprises a distributor device with medium feed so that the media are distributed uniformly over all parallel cooling/heating tubes.
 13. Device according to claim 12, wherein the distributor device has a trapezoidal inner space in which a trapezoidal volume element with smaller dimensions is arranged.
 14. Device according to claim 11, wherein the inner tube is connected to a water feed as the medium of a first thermal conductivity and the intermediate space is connected to an air feed as the medium of second thermal conductivity. 